If atoms and molecules that make up a solid vibrate, why does the solid not vibrate? What causes the solid object to not vibrate?

Question

Atoms and molecules that make up a solid vibrate. However, do the vibrations cancel each other out and that is why the solid object itself doesn’t vibrate?

Answer 1

The short answer is that solids do vibrate, but an imperceivable amount.

The longer answer depends on what you mean by "solids vibrate".

Meaning 1: A solid vibrates if I can feel a vibration while holding it.

In this sense solids DO NOT vibrate.

We cannot feel the random vibrations of its molecules because the molecules of our sensing organs also randomly vibrate.

Meaning 2: A solid vibrates if I can feel any results of its vibration while holding it.

In this sense solids DO vibrate.

When you feel the temperature of an object you are sensing the vibration of its molecules.

Meaning 3: A solid vibrates if some instruments can detect vibration of its molecules.

In this sense solids DO vibrate.

There are many instruments sensitive enough to detect the vibration of molecules.

In many experiments this is actually a problem -- the whole apparatus must be kept very cold

because the vibration of its molecules would interfere with the experiment.

Meaning 4: A solid vibrate if its center of mass vibrates.

In this sense solids DO vibrate.

The instantaneous position of the center of mass is a certain sum of the positions of its atoms.

Each atom vibrates randomly, and the amount of vibration can be represented by something called a "variance".

It turns out that what you add many random vibrations the result vibrates with variance smaller than

the variance of the individual atoms.

Therefore the larger the object the smaller is the vibration of its center of mass.